Having great power (6)
I believe the answer is:
potent
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">having great power</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for potent that I've seen before include "Strong in operation" , "Powerful, influential" , "Intoxicating" , "Strong or concentrated, like some drink" , "Powerful like strong drink" .)